Patients with myocardial ischemia typically experience angina pectoris. Activation of cardiac sympathetic afferents during ischemia is responsible for conveying cardiac nociception and initiating cardiovascular reflexes, which lead to hemodynamic alterations and arrhythmias. However, the mechanisms of activation of cardiac nociceptors are not fully understood. Endothelin-l (ET-1) and cyclooxygenase-2 products are produced early during myocardial ischemia. but their contributions to activation of cardiac nociceptors during ischemia remain uncertain. Therefore, we propose to test the following novel hypotheses: 1. Myocardial interstitial prostaglandins are increased during ischemia due to stimulation of the cyclooxygenase-2 pathway, which plays a significant role in activation of cardiac sympathetic afferents during ischemia. 2. Production of ET-1 in myocardial interstitium is increased during ischemia; an increased cardiac interstitial ET- 1 level elicits generation of prostaglandins through cyclooxygenase-2. 3. ET- 1 selectively stimulates ischemically sensitive cardiac afferents through activation of ETA, but not ETB, receptors; the stimulating effect of ET-l on ischemically sensitive cardiac afferents is mediated by prostaglandins due to activation of cyclooxygenase-2. 4. Endogenously produced ET- 1 during myocardial ischemia contributes to ischemic stimulation of cardiac sympathetic afferents. The techniques of cardiac microdialysis and single-unit recording of cardiac sympathetic afferents will be used to explore the mechanisms of generation of prostaglandins and ET-1 during myocardial ischemia, and to study the role of ET-1 and cyclooxygenase-2 in ischemic stimulation of cardiac sympathetic afferents. These studies are important prerequisites for the understanding of the pathophysiological role of ET-1 and prostaglandins in activation of cardiac nociceptors and elaborating the perception of chest pain in patients with myocardial ischemia. Such information could also suggest alternate interventions designed to treat intractable angina pectoris and to limit potentially detrimental cardiovascular reflexes in patients with coronary artery disease.